The present invention relates to pharmaceutical compositions and methods useful for modulating angiogenesis and for inhibiting metastasis and fibrosis in a mammalian tissue. The present invention further relates to a method of assessing the malignancy of colon tumors and predicting the prognosis of colon cancer.
Angiogenesis
In an adult, formation of new blood vessels in normal or diseased tissues is regulated by two processes, recapitulated vasculogenesis (the transformation of pre-existing arterioles into small muscular arteries) and angiogenesis, the sprouting of existing blood vessels (which occurs both in the embryo and in the adult).
The process of angiogenesis is regulated by biomechanical and biochemical stimuli. Angiogenic factors such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are released by vascular cells, macrophages, and cells surrounding blood vessels. These angiogenic factors activate specific proteases that are involved in degradation of the basement membrane. As a result of this degradation, vascular cells migrate and proliferate thus leading to new blood vessel formation. Peri-endothelial cells, such as pericytes in the capillaries, smooth muscle cells in larger vessels and cardiac myocytes in the heart are recruited to provide maintenance and modulatory functions to the forming vessel.
The establishment and remodeling of blood vessels is controlled by paracrine signals, many of which are mediated by protein ligands which modulate the activity of transmembrane tyrosine kinase receptors. Among these molecules are vascular endothelial growth factor (VEGF) and its receptor families (VEGFR-1, VEGFR-2, neuropilin-1 and neuropilin-2), Angiopoietins 1-4 (Ang-1, Ang-2 etc.) and their respective receptors (Tie-1 and Tie-2), basic fibroblast growth factor (bFGF), platelet derived growth factor (PDGF), and transforming growth factor β (TGF-β).
The growth of solid tumors is limited by the availability of nutrients and oxygen. When cells within solid tumors start to produce angiogenic factors or when the levels of angiogenesis inhibitors decline, the balance between anti-angiogenic and angiogenic influences is perturbed, initiating the growth of new blood vessels from the existing vascular bed into the tumor. This event in tumor progression is known as the angiogenic switch (Folkman, 1990; Hanahan and Folkman 1996). It had been demonstrated that inhibitors of tumor angiogenesis are able to completely inhibit tumor growth in mice (Boehm et al., 1997; Bergers et al., 1999) and also inhibit tumor metastasis, a process that relies upon close contact between the vasculature and tumor cells (Zetter, 1998). It has also been demonstrated that angiogenesis plays an important role in the progression of breast cancer (Weidner, N. 1998; Degani et al., 1997; Guidi et al., 1997; Balsari et al., 1999).
Such findings have prompted the use of known anti-angiogenic factors in breast cancer therapy (Klauber et al., 1997; Harris et al., 1996; Weinstatsaslow et al., 1994) and a search for novel angiogenesis inhibitors.
During the past decade several novel inhibitors of angiogenesis have been isolated including inhibitors of VEGF signaling (Neufeld et al., 1999) and inhibitors of processes which lead to the maturation and stabilization of new blood vessels. Anti-integrin antibodies have been used as inhibitors of blood vessel maturation (Brooks et al., 1994; Brooks et al., 1998).
Although several anti-angiogenic drugs are now available commercially, the anti-angiogenic mechanisms of most of these drugs (e.g., angiostatin and endostatin) remain unclear (O'Reilly et al., 1997; Oreilly et al., 1996).
Since angiogenesis can be initiated by many (possibly compensatory) angiogenic factors it stands to reason that anti-angiogenic factors which target later processes in the angiogenic response such as vessel maturation or a combination of anti-angiogenic factors would be most effective in arresting vessel formation.
Platelet factor-4 (PF4) is an anti-angiogenic protein normally sequestered in platelets (Tanaka et al., 1997; Maione et al., 1990; Neufeld et al., 2000). PF4 inhibits angiogenesis using poorly defined mechanisms (Gengrinovitch et al., 1995; Brown, and Parish, 1994; Gupta, and Singh, 1994; Watson et al., 1994). It was previously speculated that PF4 binds to cell surface heparan-sulfate proteoglycans and in this manner inhibits the activity of angiogenic growth factors such as basic fibroblast growth factor (Watson et al., 1994).
Tumor Metastasis and Staging
The transition from a localized tumor to an invasive and metastatic tumor represents a landmark in the development of malignant disease, since it is usually associated with a markedly worse prognosis. The understanding of the processes that govern this transition is therefore of prime importance.
Breast Cancer
In breast cancer, the transition from a localized to an invasive/metastatic tumor is associated in many cases with the formation of fibrotic foci and desmoplasia, which is the presence of unusually dense collagenous stroma, within the primary tumor (Colpaert et al., 2001; Hasebe et al., 2000). A similar correlation may exist in other types of cancers such as colon and pancreatic cancers (Nishimura et al., 1998; Ellenrieder et al., 2000). These observations represent apparent paradoxes at first glance, since invasiveness has long been associated with the destruction of extracellular matrix by extracellular matrix degrading enzymes like metalo-proteases (Stamenkovic, 2000; Duffy et al., 2000) and heparanase (Vlodavsky and Friedmann, 2001). However, it is possible that deposition of excess extracellular matrix may stimulate in turn expression of matrix degrading enzymes that will contribute under certain circumstances to tumor invasion. In fact, there is some evidence that an increase in extracellular matrix deposition can indeed influence the production of extracellular matrix degrading enzymes (Schuppan et al., 2001; Swada et al., 2001).
Several prior art studies have attempted to develop agents to treat breast cancer metastases (Sauer et al., 2002) including a study by Kim et al., (2000) that described apicidin [cyclo(N—O-methyl-L-tryptophanyl-L-isoleucinyl-D-pipecolinyl-L-2-amino-8-oxodecanoyl)], a fungal metabolite that was identified as an antiprotozoal agent known to inhibit parasite histone deacetylase (HDAC), that can inhibit the H-ras-induced invasive phenotype of MCF10A human breast epithelial cells. Another agent is the polymeric form of fibronectin that was shown to reduce tumor growth and to posses antimetastatic activity when administered systemically to tumor-bearing mice (Yi and Ruoslahti, 2001).
Colon Cancer
Cancer of the gastrointestinal (GI) tract, especially colon cancer, is a highly treatable and often a curable disease when localized to the bowel. Surgery is the primary treatment and results in cure in approximately 50% of patients. Recurrence following surgery is a major problem and often is the ultimate cause of death. Nearly all cases of colorectal cancer arise from adenomatous polyps, some of which mature into large polyps, undergo abnormal growth and development, and ultimately progress into cancer. This progression would appear to take at least 10 years in most patients, rendering it a readily treatable form of cancer if diagnosed early, when the cancer is localized.
The standard procedures currently used for establishing a definitive diagnosis for a GI tract cancer include barium studies, endoscopy, biopsy and computed tomography [M. F. Brennan, et al. In: Cancer: Principles and Practice of Oncology, Fourth Edition, pp. 849-882, Philadelphia, Pa.: J. B. Lippincott Co. (1993)].
The prognosis of colon cancer is clearly related to the degree of penetration of the tumor through the bowel wall and the presence or absence of nodal involvement. These two characteristics form the basis for all staging systems developed for this disease. Staging is usually performed by a pathologist on tissue sections obtained via biopsy and/or surgery and it aims to determine the anatomic extent of the disease. Accurate staging is critical for predicting patient outcome and providing criteria for designing optimal therapy. Inaccurate staging can result in poor therapeutic decisions and is a major clinical problem in colon cancer.
Thus, to increase the accuracy of therapy and the survival rate of colon cancer patients there is a need to develop sensitive and accurate methods of staging of colon cancer.